Book/Dissertation / PhD Thesis

FZJ-2017-03840

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Chemical and physical properties of sodiumionic conductors for solid-state batteries

Guin, M. (Corresponding author)FZJ*

2017
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag Jülich
ISBN: 978-3-95806-229-0

Please use a persistent id in citations: http://hdl.handle.net/2128/14636

Abstract: The electrochemical storage of electricity in batteries is one key solution to the future extensive use of renewable energy sources. Lithium ion batteries have received intense attention since they provide the largest energy density and output voltage. They have yet to be optimized in terms of capacity, safety and cost and the search for alternatives to lithium has already gained popularity in the past years because of the shortage of resources. One popular substitute is sodium since its chemical properties are similar to those of lithium and sodium is an abundant element. Sodium technologies are not new but the commercial sodium-ion batteries operate at temperatures as high as 300 °C raising safety issues and discussion about the energy needed to heat the battery. Therefore, solid-state sodium batteries operating at room temperature present a safer alternative as they are leak proof and non-flammable. In addition, no supplementary heating equipment is needed to operate the battery. The key in designing safe and efficient solid-state Na-ion batteries is the development of highly conductive solid electrolytes that also display high thermal and chemical stability. Amongst all possibilities, one class of ceramic electrolytes is of great interest: the so-called NASICON materials with general formula AM(PO$_{4)3}$ (in this work, A = Na). They display very attractive compositional diversity and are likely to achieve high conductivity. In this thesis, an extensive study of the composition, the crystal structure and the conductivity of approximately 110 Na-conducting NASICON materials was conducted to find guidelines for designing highly conductive NASICON type materials. For NASICON with aliovalent substitution, the electroneutrality is guaranteed by adapting the amount of Na per formula unit and an optimal Na concentration of 3.2-3.5 mol was identified. Furthermore, an optimal size for the M cations in the structure was highlighted. In addition, the substitution of P with Si proved to have a positive impact on the conductivity. Using these guidelines, the solid solution Na$_{3+x}$Sc$_{2}$(SiO$_{4)x}$(PO$_{4)3-x}$ was investigated for the first time. Various compositions with 0 $\le$ x $\le$ 0.8 were prepared by solid state reaction and their crystallographic and electrical properties were investigated. As a result, the high conductivity at room temperature of 8.3 x 10$^{-4}$ S cm$^{-1}$ was obtained for x = 0.4. In addition, the criteria for high conductivity concluded from the literature study were verified and completed with data of bulk conductivity for the solid solution. This systematic study of the substitution of P with Si provided better insights in the conduction pathway of the sodium ions in the NASICON structure. Finally, thick, dense pellets of Na$_{3.4}$Sc$_{2}$Si$_{0.4}$P$_{2.6}$O$_{12}$ were used as solid electrolyte in different solid-state battery designs and for the first time, a solid-state Na battery based on inorganic materials was cycled at room temperature.

Note: RWTH Aachen, Diss., 2017

---

Contributing Institute(s):

1. Werkstoffsynthese und Herstellungsverfahren (IEK-1)

Research Program(s):

1. 131 - Electrochemical Storage (POF3-131) (POF3-131)

Appears in the scientific report 2017

---

Database coverage:
;

---